Mechanical marine steering systems are frequently of the rack and pinion gear type. Such steering systems usually include a rotary gear (i.e., pinion gear) rotatably engaging an output gear (i.e., rack gear) in response to rotation from a steering wheel. The output gear typically includes a cable attached thereto as attached to a rudder or an outdrive of a marine engine for remotely controlling the movement thereof. The rudder or outdrive usually pivots about a vertical axis for directing the flow of water thereby.
As the rudder or outdrive rotation increases, the flow supplied by the passing water increases to likewise increase the required steering input force. In other words, as the rudder increasingly becomes transverse to the water flow, the force (i.e., drag) placed on the rudder by the passing water increases. This, in turn, increases the torque necessary to rotate the steering wheel.
In known prior art steering systems, the increasing rudder forces are overcome by providing a plurality of gearing mechanism, most of which require manual shifting between gears by the operator.
The U.S. Pat. No. 3,225,620 issued to Dubin discloses a multiple ratio steering system including a steering shaft with a beveled gear attached on the end thereof. The beveled gear engages with a second beveled gear connected to a shaft which, in turn, rotates a pair of spur gears. The spur gears are slideable along the shaft by means of a key connected to an adjustment rod. The first spur gear is engaged with a first pinion gear, or the second spur gear is engaged with a second pinion gear, depending on the desired steering ratio. The rotation of both pinion gears is about a second shaft having a screw gear attached thereon. The screw gear rotation is translated to an output shaft gear, thus causing rotation of an output shaft. A major deficiency in this system is that the variable ratio depends on the manual selection of four different gears mounted concentrically on two different shafts.
The U.S. Pat. No. 4,244,316 to Kulischenko discloses an input shaft connected to a steering wheel having a key thereon. The input shaft can be locked in either one or two different positions by engaging pins. In the first position, the input shaft having the key thereon engages the driver pulley causing a driven pulley to rotate by virtue of a timing belt operatively engaged therebetween. The driven pulley is provided with a smaller diameter than the driver pulley and thus, a single revolution of driver pulley will produce a plurality of revolutions of the driven pulley. The driven pulley rotates about the same shaft as a second driver pulley. The second driver pulley causes a second driven pulley to rotate therewith by virtue of a second timing belt operatively engaged therebetween. Similarly, a single revolution of the second driver pulley will produce a plurality of revolutions of the second driven pulley. Thus, the Kulischenko patent discloses six revolutions of the second driven pulley with one revolution of the steering wheel. With the input shaft in the first position, the operator is given a mechanical advantage through a plurality of pulley-belt systems. In addition, when the input shaft is in the second position, the key is disengaged from the pulley-belt system thereby directly rotating the output shaft. The Kulischenko system, however, has the similar deficiency of requiring the operator to manually select between a plurality of gearing mechanisms to selectively increase or decrease the mechanical advantage.